The hypotheses of the study are that alosetron decelerates colonic transit greater in female patients as compared to male patients with nonconstipated IBS, and that alosetron decelerates small bowel transit and gastric emptying in patients with nonconstipated IBS. The specific aims of the study are to measure gastric emptying, small bowel and colonic transit in 15 male and 15 female patients with nonconstipated IBS before and during treatment with alosetron, 1 mg, for six weeks.